1. Field of the Invention
The present invention relates to a method of correcting the partially worn die mounting surfaces of the platens of a die casting machine and, more specifically, to a method of correcting the partially worn die mounting surfaces of the cast iron or cast steel platens of a die casting machine.
2. Description of the Related Art
The die mounting surfaces of the stationary platen and the movable platen (which will be referred to inclusively as "platens"), formed of cast iron or cast steel used on a die casting machine in an aluminum die casting foundry are subject to partial wear. The depth of partial wear in several years of service is in the range of about 0.3 to 4 mm with the die mounting surface of the stationary platen (hereinafter, referred to as "stationary die mounting surface") and in the range of about 0.3 to 4 mm with the die mounting surface of the movable platen (hereinafter, referred to as "movable die mounting surface"). Accordingly, the partial clearance, i.e., the clearance which is formed when the stationary platen and the movable platen are joined together between the partially worn stationary die mounting surface of the stationary platen and the partially worn movable die mounting surface of the movable platen, is in the range of about 0.3 to about 8 mm.
When the stationary die mounting surface and the movable die mounting surface are partially worn in such a depth, the clamping pressure is applied unevenly to the die, and consequently, casting fins are formed. Casting fins clog the air vent grooves of the die, causing air to be entrapped in the molten metal and causing backflash. Backflash entails loss in the following process and defects in the casting, and may cause troubles. The stationary die mounting surface and the movable die mounting surface must be always kept in a high flatness to prevent such problems.
Around the time when such problems are liable to occur, the partial wear in the surfaces of the platens, i.e., the stationary die mounting surface and the movable die mounting surface, is corrected. Generally, the partial wear in the surfaces of the platens is corrected by a surface correcting method including taking the die casting machine apart to remove the platens from the die casting machine, transporting the platens to the machining shop of the maker of the die casting machine or to the maintenance shop of the die casting machine, machining the surfaces of the platens by an ordinary face cutting machine, such as a shaper, installed in the machining shop to finish the partially worn surfaces of the platens in a high flatness, transporting the thus finished platens to the die casting foundry, and mounting the platens on the die casting machine. The die mounting surfaces of the platens must be finished in a flatness within 1/10 mm.
The recent change in the mold lubricant for lubricating the die held on the platens of the die casting machine, namely, the replacement of oil mold lubricants with water mold lubricants, to prevent fire hazard has reduced the service time in which the depth of partial wear in the die mounting surfaces of the platens increases to a limit. The service time was in the range of about five years to about six years when oil mold lubricants were used, whereas the service time is only about one year when water mold lubricants are used. Therefore, the partial wear in the die mounting surfaces of the platens must be corrected more frequently in recent years than before.
The aforesaid conventional surface correcting method has problems that the correction of the die mounting surfaces needs many steps, requires a very long time in the range of one month to three months from the first step of taking the die casting machine apart to the last step of mounting the platens on the die casting machine, troublesome work for taking the die casting machine apart and assembling the same and much expenses, and hence is economically disadvantageous. Since the service time in which the partial wear in the die mounting surfaces of the platens increases to a limit has been reduced and the die mounting surfaces of the platens need more frequent correction than before, the foregoing problems are more serious problems in recent years.